Composite, carbon composite including the composite, electrode, lithium battery, electroluminescent device, biosensor, semiconductor device, and thermoelectric device including the composite and/or the carbon composite

ABSTRACT

A composite including: silicon (Si); a silicon oxide of the formula SiOx, wherein 0&lt;x&lt;2; and a graphene disposed on the silicon oxide.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of application Ser. No.14/499,624, filed Sep. 29, 2014, which claims priority to and thebenefit of Korean Patent Application Nos. 10-2013-0116892, filed on Sep.30, 2013, and 10-2014-0119376, filed on Sep. 5, 2014, in the KoreanIntellectual Property Office, and all the benefits accruing therefromunder 35 U.S.C. § 119, the contents of which are incorporated herein intheir entirety by reference.

BACKGROUND

1. Field

The present disclosure relates to a composite, a carbon compositeincluding the composite, and an electrode, a lithium battery, anelectroluminescent device, a biosensor, a semiconductor device, and athermoelectric device including the composite or the carbon composite.

2. Description of the Related Art

Silicon, among negative electrode active materials for a lithium ionbattery, has been studied for use as a negative electrode material sincesilicon has a high theoretical capacity of 4200 milliampere-hours pergram (mAh/g) and a low cost. However, silicon undergoes a large volumeexpansion when alloyed with lithium during discharge of a battery toform Li_(4.4)Si. The silicon active material is understood to becomeelectrically isolated from the electrode as a result of pulverizationdue to the large volume expansion. Also, an electrolyte dissociationreaction is increased as a specific surface area of the siliconincreases due to the volume expansion. In this regard, a structure thatreduces the volume expansion of the silicon and has less of thepulverization phenomenon during the volume expansion has been developed.

However, when an available silicon material is used, a volume expansionand battery charging/discharging efficiency are still not satisfactory.Thus there remains a need for an improved silicon negative electrodeactive material.

SUMMARY

Provided is a composite.

Provided is a method of manufacturing the composite.

Provided is a carbon composite including the composite and acarbon-based material.

Provided is an electrode including the composite and/or the carboncomposite including the composite and a carbon-based material.

Provided is a lithium battery including the electrode.

Provided is an electroluminescent device including the composite and/orthe carbon composite including the composite and a carbon-basedmaterial.

Provided is a biosensor including the composite and/or the carboncomposite including the composite and a carbon-based material.

Provided is a semiconductor device including the composite and/or thecarbon composite including the composite and a carbon-based material.

Provided is a thermoelectric device including the composite and/or thecarbon composite including the composite and a carbon-based material.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description.

According to an aspect, a composite includes: silicon (Si); a siliconoxide of the formula SiOx disposed on the silicon, wherein 0<x<2; and agraphene disposed on the silicon oxide.

According to another aspect, a method of manufacturing a compositeincludes: supplying a reaction gas to a structure including a siliconand a silicon oxide of the formula SiOx, wherein 0<x<2; andheat-treating the reaction gas and the structure to manufacture thecomposite.

According to another aspect, a carbon composite includes the compositeand a carbonaceous material.

According to another aspect, an electrode includes the composite.

According to another aspect, an electrode includes the carbon compositeincluding the composite and the carbonaceous material.

According to another aspect, a lithium battery includes the electrode.

According to another aspect, a device includes the composite.

According to another aspect, a device includes the carbon compositeincluding the composite and the carbonaceous material.

The device is one of an electroluminescent device, a biosensor, asemiconductor device and a thermoelectric device.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIGS. 1A and 1B are each a schematic illustration of an embodiment inwhich graphene in the form of a nanosheet is disposed on a silicon oxidewhich is disposed on silicon wires;

FIGS. 1C and 1E illustrates a method of implementing a clamping effectas a graphene layer helps silicon particles to expand and lithium ionsto diffuse during a lithiation process, and FIG. 1D illustrates acomposite that may be used as a negative electrode active material andis lithiated;

FIG. 2A is a schematic view of an embodiment of a lithium battery;

FIG. 2B is a schematic diagram of an embodiment of a thermoelectricmodule;

FIG. 2C is a schematic diagram illustrating an embodiment of athermoelectric cooler that uses the Peltier effect;

FIG. 2D is a schematic diagram illustrating an embodiment of athermoelectric generator that uses the Seebeck effect;

FIG. 2E illustrates a structure of an embodiment of an electrode of abiosensor;

FIG. 3 is a graph of capacity (milliampere-hours, mAh) versus number ofcycles which shows discharge capacity change in coin cells prepared inManufacturing Example 1 and Comparative Manufacturing Examples 1 and 2,which included negative electrodes prepared in Example 1 and ComparativeExamples 1 and 2, respectively;

FIG. 4 is a graph of capacity (milliampere-hours, mAh) versus number ofcycles which shows discharge capacity change in coin cells prepared inManufacturing Examples 1 to 5 and Comparative Manufacturing Examples 1and 3 and Reference Manufacture Example 1, which included negativeelectrodes prepared in Examples 1 to 5 and Comparative Examples 1 and 3,and the composite prepared in Reference Example 1, respectively;

FIG. 4A is a graph of rate performance evaluation of coin cells preparedin Manufacturing Example 8 and Comparative Manufacturing Examples 7 and8;

FIG. 5 is a graph of capacity retention rate (percent, %) versus numberof cycles which shows a change in capacity in coin cells prepared inManufacturing Example 1 and Comparative Manufacturing Examples 1 and 2;

FIG. 6 is a graph of capacity retention rate (percent, %) versus numberof cycles which shows change in capacity in coin cells prepared inManufacturing Examples 1 to 5, Comparative Manufacturing Examples 1 and3, and Reference Manufacturing Example 1;

FIG. 6A is a graph showing charge and discharge characteristics of thecoin cells prepared in Manufacturing Example 8 and ComparativeManufacturing Examples 7 and 8;

FIGS. 7A, 8A, and 9A show the results of transmission electronmicroscope (TEM) analysis performed on a composite prepared inPreparation Example 1 and materials prepared in Comparative PreparationExamples 1 and 2, respectively;

FIGS. 7B, 8B, and 9B are enlarged views of FIGS. 7A, 8A, and 9A,respectively;

FIGS. 8C to 8E show the results of transmission electron microscopeanalysis of a composite prepared in Preparation Example 8;

FIG. 8F is an electron energy loss spectroscopy (EELS) spectra of thecomposite of FIG. 8E;

FIGS. 10 and 12A, 13A, 14A, 15A, 16A and 17A are images from TEManalysis of the composites prepared in Preparation Examples 2 to 5, thematerials prepared in Comparative Preparation Examples 1 and 3, and amaterial prepared in Reference Example 1, respectively;

FIGS. 11 and 12B, 13B, 14B, 15B, 16B, and 17B are enlarged views ofFIGS. 10 and 12A, 13A, 14A, 15A, 16A and 17A, respectively;

FIGS. 18A to 18C are graphs of intensity (arbitrary units, a.u.) versusbinding energy (electron volts, eV) illustrating the results of X-rayphotoelectron spectroscopy (XPS) analysis performed on the compositeprepared in Preparation Example 1 and the materials prepared inComparative Preparation Examples 1 and 2, respectively;

FIGS. 19A to 19C are graphs of intensity (arbitrary units, a.u.) versusbinding energy (electron volts, eV) which illustrate the results of XPSanalysis performed on the composites prepared in Preparation Examples 1to 4, the materials prepared in Preparation Examples 6 and 7, and amaterial prepared in Comparative Preparation Example 1, respectively;

FIGS. 20A and 20B illustrate the results of TEM-EDAX analysis performedon the composite prepared in Preparation Example 1, in which FIG. 20B isa graph of intensity (counts) versus location (nanometers, nm);

FIGS. 21A and 21B illustrate the results of Energy Dispersive X-raymicroanalysis (TEM-EDAX) analysis performed on the material prepared inComparative Preparation Example 1, in which FIG. 21B is a graph ofintensity (counts) versus location (nanometers, nm);

FIGS. 22A and 22B illustrate the results of TEM-EDAX analysis performedon the material prepared in Comparative Preparation Example 2, in whichFIG. 22B is a graph of intensity (counts) versus location (nanometers,nm);

FIG. 23 is a graph of thermogravimetric weight loss (percent) andderivative thermogravimetric weight loss (percent per degree centigrade,%/° C.) versus temperature (° C.) illustrating the results ofthermogravimetric analysis performed on the composites prepared inPreparation Examples 1 to 3;

FIG. 24 is a graph of intensity (arbitrary units, a.u.) versusdiffraction angle (degrees two-theta, 2θ) illustrating the results ofX-ray analysis performed on the composites prepared in PreparationExamples 1 to 3 and the material prepared in Comparative PreparationExample 1;

FIG. 25 is a graph of intensity (arbitrary units, a.u.) versus Ramanshift (inverse centimeters, cm⁻¹) illustrating the results of Ramananalysis performed on the composites prepared in Preparation Examples 1to 3 and the material prepared in Comparative Preparation Example 1;

FIGS. 26A, 27A, and 28A are scanning electron microscope images ofcomposites prepared in Preparation Examples 8 and 9 and ComparativePreparation Example 4, respectively;

FIGS. 26B, 26C, 27B, and 28B are enlarged views of FIGS. 26A, 27A, and28A, respectively; and

FIGS. 29A to 29E show the results of In-situ TEM analysis using thecomposite prepared in Preparation Example 8.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the presentembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theembodiments are merely described below, by referring to the figures, toexplain aspects of the present description. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items. “Or” means “and/or.” Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present.

It will be understood that, although the terms “first,” “second,”“third,” etc. may be used herein to describe various elements,components, regions, layers, and/or sections, these elements,components, regions, layers, and/or sections should not be limited bythese terms. These terms are only used to distinguish one element,component, region, layer, or section from another element, component,region, layer, or section. Thus, “a first element,” “component,”“region,” “layer,” or “section” discussed below could be termed a secondelement, component, region, layer, or section without departing from theteachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ±30%, 20%, 10%, 5% of the stated value.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

A C rate means a current which will discharge a battery in one hour,e.g., a C rate for a battery having a discharge capacity of 1.6ampere-hours would be 1.6 amperes.

“Rare earth” means the fifteen lanthanide elements, i.e., atomic numbers57 to 71, plus scandium and yttrium.

The term “graphene” as used in the present specification means apolycyclic aromatic molecule formed from a plurality of carbon atomswhich are covalently bound to each other. The covalently bound carbonatoms may form a six-membered ring as a repeating unit, and may furtherinclude at least one of a five-membered ring and a seven-membered ring.Accordingly, graphene comprises a single layer of covalently bondedcarbon atoms having sp² hybridization. A plurality of graphene layers isoften referred to in the art as graphite. However, for convenience,“graphene” as used herein may be a single layer, or also may comprise aplurality of layers of carbon. Thus graphene, as used herein, may have amultiply layered structure formed by stacking single layers of graphene.

By referring to the accompanying drawings, a composite, a method ofmanufacturing the composite, a carbon composite including the compositeand a carbon-based material, an electrode active material including thecomposite and/or the carbon composite, a lithium battery including theelectrode active material, and an device including the composite and/orthe carbon composite including the composite and a carbon-basedmaterial, will be disclosed in further detail.

The device is one of an electroluminescent device, a biosensor, asemiconductor device and a thermoelectric device.

Provided is a composite comprising silicon (Si); a silicon oxide of theformula SiOx, wherein 0<x<2, disposed on the silicon; and graphenedisposed on the silicon oxide.

When silicon nanowires are used as an electrode active material, thesilicon nanowires are disposed on, e.g., attached to, a surface of aconducting material, such as graphite. A volume expansion of the siliconoccurs as the silicon is lithiated. As a result, and while not wantingto be bound by theory, it is understood that when the battery isrepeatedly charged and discharged, lithium is consumed to form a newsolid electrolyte interface (SEI) layer as the silicon is pulverized,and thus durability of the battery is degraded due to a decrease in acapacity of the battery, e.g., due to loss of lithium to the SEI layerand disconnection of the silicon nanowires.

The composite comprises graphene disposed on, e.g., grown on, thesilicon oxide of the formula SiOx, wherein 0<x<2. The silicon oxide maybe a natural oxide layer, which is present on the silicon. While notwanting to be bound by theory, it is understood that the silicon oxideresolves the degradation of durability of a battery described above. Thecomposite allows the graphene, which has excellent conductivity andflexibility, to suppress and/or accommodate the volume expansion of thesilicon. The graphene can be grown directly on a surface of the silicon,and thus volume expansion may be suppressed, and the pulverizing of thesilicon may be reduced. Also, opportunities for the silicon to directlycontact an electrolyte may be reduced by using the graphene, and thusgeneration of the SEI layer may be reduced.

When graphene is formed on silicon by an alternative method, siliconoxide, which is a natural oxide layer on the silicon, is first reducedto form silicon, and then the silicon is contacted with acarbon-containing gas to form the graphene. According to the alternativemethod, a carbide material, such as silicon carbide (SiC), may be formedon the silicon, and the graphene is formed thereon. However, whengraphene is formed on surface on which a carbide material, such as SiC,is formed directly on the surface of the silicon, SiC does not reactwith Li. Thus, when a composite including SiC is used as an electrodematerial, capacity development is deteriorated, and thus a capacity isreduced. Also, since a temperature of 1400° C. or higher may be used toform the graphene on the SiC, a Si crystallinity increases, and thussilicon pulverization is accelerated during charging and discharging ofa battery using an electrode including the electrode material. It hasbeen surprising discovered that a shape, a structure, and a thickness ofgraphene may be controlled when the graphene on the silicon is formed byusing a silicon oxide of the formula SiOx, wherein 0<x<2, as a seedlayer for forming the graphene, rather than removing the silicon oxide,which is a natural oxide formed on the silicon.

The silicon oxide (SiOx, wherein 0<x<2), is an unstable material whichlacks oxygen, as compared to silica (i.e., SiO₂), and has a tendency toform a stable material by reacting with another reactive material, suchas carbonaceous source gas. By applying this tendency of the siliconoxide, the silicon oxide (SiOx, wherein 0<x<2) may be used as a seedlayer for forming graphene.

A thickness of the silicon oxide (SiOx, wherein 0<x<2) formed on thesilicon significantly affects a shape and/or a structure of thegraphene.

A thickness of the silicon oxide (SiOx, where 0<x<2) may be selected byusing a manufacturing process used in formation of graphene, forexample, by using a carbonaceous source gas suitable for formation ofgraphene. A thickness of the silicon oxide (SiOx, wherein 0<x<2) may beabout 300 μm or less.

According to an embodiment, a thickness of the silicon oxide (SiOx,wherein 0<x<2), where the composite is included in a battery, may beabout 10 nm or less, for example, in a range of about 0.1 nm to about 10nm, or about 0.1 nm to about 5 nm. When a battery includes a compositehaving a layer of the silicon oxide (SiOx, wherein 0<x<2) with athickness within these ranges above, the battery may have excellentcapacity characteristics.

According to an embodiment, the graphene is formed on the silicon oxide(SiOx, wherein 0<x<2) of the silicon by gaseous carbon deposition thatdoes not use a catalyst.

The gaseous carbon deposition is performed by heat-treating silicon thatis covered with a silicon oxide (SiOx) under gas atmosphere, wherein thegas is at least one selected from a compound represented by Formula 1, acompound represented by Formula 2, and an oxygen-containing gasrepresented by Formula 3.C_(n)H_((2n+2−a))[OH]_(a)  Formula 1In Formula 1, n is an integer of 1 to about 20, and a is an integer of 0or 1.C_(n)H_((2n))  Formula 2In Formula 2, n is an integer of about 2 to about 6.C_(x)H_(y)O_(z)  Formula 3

In Formula 3, x is 0 or an integer of 1 to about 20, y is 0 or aninteger of 1 to about 20, and z is an integer of about 1 or about 2.

The gaseous carbon deposition is not limited to the theory that isdisclosed herein. The coating formed by the gaseous carbon deposition isrelated to reforming of the silicon covered with the silicon oxide(SiOx) using CO₂. For example, when the compound represented by Formula1 is methane (i.e., n is 1 and a is 0 in Formula 1), it is understoodthat carbon deposition may occur on a composite oxide on the basis of areaction (e.g., a Boudouard reaction of Reaction Scheme 2) that occursas a side reaction of a modification reaction of Reaction Scheme 1.Also, it may be understood that carbon deposition generated by adecomposition reaction of the compound represented by Formula 1, forexample, in the case of methane, the reaction of Reaction Scheme 3.CH₄+CO₂↔2H₂+2CO  Reaction Scheme 12CO↔CO₂+C  Reaction Scheme 2CH₄↔2H₂+C  Reaction Scheme 3

However, the reaction that may occur during the heat-treating of thecarbon coating method is not limited to the reaction described above,and reactions other than the foregoing reaction may occur.

According to the gaseous carbon deposition, graphene is grown directlyon silicon, which is covered partially or entirely with silicon oxide(SiOx), and thus silicon and graphene are highly adhered to each other.The silicon oxide may cover about 1 to 100%, about 5% to about 95%, orabout 10% to about 90% of an area of the silicon.

According to another embodiment, even when an SiOx layer is not presenton the silicon, an SiOx layer may be first formed on the silicon byreaction with an oxygen containing gas or gas mixture, and then graphenemay be formed thereon by reaction of reaction gas and the oxygencontaining gas, for example.

An adherency between the silicon and the graphene may be evaluated byusing a distance between the silicon and the graphene as determined witha scanning electron microscope (SEM). The distance between the grapheneand the silicon may be about 10 nm or less, for example, or about 0.5 nmto about 10 nm. In some embodiments, the graphene is a distance of about1 nm or less, for example, about 0.5 nm to about 1 nm, from the silicon.In another embodiment, an adherency between the silicon oxide and thegraphene may be evaluated by using a distance between the silicon oxideand the graphene as determined with a scanning electron microscope(SEM). The distance between the graphene and the silicon oxide may beabout 10 nm or less, for example, or about 0.5 nm to about 10 nm. Insome embodiments, the graphene is a distance of about 1 nm or less, forexample, about 1 nm or less, for example, about 0.5 nm to about 1 nm,from the silicon oxide. Also, the graphene may be oriented at an anglein a range of about 0° to about 90°, or about 5° to about 80°, forexample about 10° to about 70°, with respect to a main axis of thesilicon. The graphene may comprise one to 20 layers of graphene, and thetotal thickness of the graphene may be about 0.6 nm to about 12 nm, forexample about 1 nm to about 10 nm, or about 2 nm to about 8 nm.

A shape of the silicon is not limited, and may be rectilinear and/orcurvilinear, and may be for example, at least one selected fromnanowires, particles, nanotubes, nanorods, wafers, and nanoribbons.

In an embodiment, the silicon may have a shape of a nanowire. Here, across-sectional diameter of a silicon nanowire may be less than about500 nm, for example, from about 10 nm to about 300 nm, for example about25 nm to about 200 nm. Alternatively, a diameter of the nanowires may begreater than about 50 nm, for example from about 50 nm to about 100 nm,or about 60 nm to about 90 nm. A length of the nanowires may be about100 nm to about 100 micrometers (μm), or about 200 nm to about 10 μm. Anaspect ratio (length/width) of the nanowires may be 2 to about1,000,000, for example about 4 to about 500,000, or about 8 to about250,000.

In an embodiment, a silicon oxide (SiOx, wherein 0<x<2) layer is formedon silicon nanowires, and graphene may be formed thereon.

In some embodiments, a silicon oxide (SiOx, wherein 0<x<2) layer isformed on silicon nanoparticles, and graphene may be formed thereon.Here, an average particle diameter of the silicon nanoparticles may befrom about 40 nm to about 40 μm, or about 40 nm to about 100 nm. Anaspect ratio of the nanoparticles may be about 1 to 2, specificallyabout 1.05 to about 1.9, for example about 1.1 to about 1.8, or about1.2 to about 1.7.

When the silicon is a wafer type, a thickness of the silicon wafer maybe 2 mm or less, for example, about 0.001 mm to about 2 mm.

The graphene is a polycyclic aromatic molecule comprising a plurality ofcarbon atoms that are covalently bonded to one another, and thecovalently bonded plurality of carbon atoms form a 6-membered ring as abasic repeating unit, but a 5-membered ring and/or a 7-membered ring maybe included in the graphene. As a result, the graphene may appear as asingle layer of the covalently bonded carbon atoms (in general, having asp² bond). The graphene may be a single layer or multiple layers ofcarbon, e.g., 1 layer to about 100 layers, for example, about 2 layersto about 100 layers or about 3 layers to about 50 layers that arestacked on each other.

The graphene may be in the form of a nanosheet or a layer.

The term “nanosheet” and “layer” used herein are defined as follows.

The term “nanosheet” denotes a structure having an irregular form.

The term “layer” denotes a structure that is continuously and uniformlydisposed on a surface, e.g., formed on a silicon oxide surface.

The FIG. 1A schematically illustrates an embodiment of a composite inwhich a graphene nanosheet 11 is formed on a sil2 icon wire 10 coveredwith a silicon oxide, and FIG. 1C schematically illustrates anembodiment of a composite on which a graphene layer 12 is formed on asilicon wire 10 covered with a silicon oxide.

The FIGS. 1B and 1D each schematically illustrate a composite that maybe used as a negative electrode active material and is lithiated.

A content of graphene in a composite in an embodiment is, about 0.001part to about 90 parts by weight, for example, about 0.01 part to about20 parts by weight, or for example, about 0.01 part to about 10 parts byweight, based on 100 parts by weight of the composite. When a content ofthe graphene is within the range above, volume change is substantiallysuppressed, and improved conductivity characteristics are provided.

The composite may further include a metal oxide. In this regard, when ametal oxide is further included in the composite, formation of a SEIlayer may be prevented due to suppression of side reaction. The metaloxide may be disposed on at least one selected from the siliconnanowire, the silicon oxide, and the graphene.

The metal oxide may comprise at least one selected from a magnesiumoxide, a manganese oxide, an aluminum oxide, a titanium oxide, azirconium oxide, a tantalum oxide, a tin oxide, and a hafnium oxide.

The composite may further include a metal fluride. The metal fluoridemay comprises an aluminum fluoride (e.g., AlF₃).

In the composite according to an embodiment, graphene may serve as anSEI stabilization clamping layer. Also, the composite has a highspecific surface area, and thus when a battery includes the composite,deterioration of an initial efficiency and a volume energy density maybe prevented.

Graphene may suppress disintegration or pulverization of an activematerial, such as silicon, and may improve conductivity of thecomposite.

FIG. 1C illustrates a method of implementing a clamping effect as agraphene layer helps silicon particles to expand and lithium ions todiffuse during a lithiation process.

A graphene encapsulation layer prevents disintegration or pulverizationof particles which typically occurs with conventional silicon particles.A graphene sliding layer serves as a clamping layer which preventsdisintegration of the silicon particles while still allowing for thealloying reaction of lithium ions with silicon to yield a significantspecific capacity, and provide a continuous conduction pathway betweenthe particles.

The graphene layers slide over each other during silicon particlesswelling, and then slide back to their relaxed positions during thedelithiation process. This is because the van der Walls force is greaterthan the friction force between layers.

The clamping effect of the graphene layers may be confirmed to serve asa clamping layer that prevents disintegration of silicon particles byexamining whether the graphene layer is maintained the same after 200lithiation/delithiation cycles.

In another aspect, a carbon composite including the composite and acarbonaceous, e.g., carbon-based, material is provided. The carboncomposite has an initial efficiency, cycle properties, and durability,which are improved compared to those of the composite.

The carbon-based material includes at least one selected from graphite,graphene, and carbon nanotubes (CNTs).

A content of the carbon-based material is about 50 parts by weight orless, for example, from about 0.0001 part to about 50 parts by weight,based on 100 parts by weight of the carbon composite. In an embodiment,a content of the carbon-based material may be from about 0.0001 part to30 parts by weight, for example, from about 0.0001 part to about 20parts by weight, based on 100 parts by weight of the carbon composite.

In another embodiment, a content of the carbon-based material is fromabout 0.001 part to about 10 parts by weight, for example, from about0.01 part to about 5 parts by weight. When a content of the carbon-basedmaterial is within the range above, a carbon composite having animproved capacity and conductivity may be obtained.

The carbon composite comprises, for example, graphite and a compositeformed on the graphite. The composite has a structure including siliconnanowires covered with a silicon oxide (SiO_(x), where 0<x<2) layer anda graphene film or a graphene nanosheet formed on the silicon oxidelayer of the silicon.

The graphite may be, for example, SFG6 graphite, available from TIMCALGraphite and Carbon of Bodio, Switzerland, and may have an averageparticle diameter of about 6 μm. The silicon nanowires may have adiameter in a range of about 50 nm to about 400 nm, for example about100 nm to about 300 nm.

When the electrode is formed by using the carbon composite, a content ofthe carbon composite in the electrode may be, for example, from about 68parts to about 87 parts by weight, for example about 70 parts to about85 parts by weight, and a content of a binder may be, for example, fromabout 13 parts to about 32 parts by weight, for example about 15 partsto about 30 parts by weight, based on a 100 parts by weight of thecarbon composite and the binder. In the carbon composite, a content ofthe graphite may be, for example, from about 1 part to about 20 parts byweight, based on 100 parts by weight of the carbon composite.

Any suitable binder may be used. Examples of the binder may include atleast one selected from a vinylidene fluoride/hexafluoropropylenecopolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile,polymethylmethacrylate, polytetrafluoroethylene, a styrene butadienerubber-based polymer, polyacrylic acid, polyamideimide, and polyimide.The binder is not limited thereto, and any suitable material availableas a binder in the art may be used. The binder may be, for example,lithium-substituted polyacrylate.

Hereinafter, a method of manufacturing a composite according to anotherembodiment will be disclosed in further detail.

The method includes disposing a carbonaceous gas, e.g., supplying acarbon source gas, on a structure including a silicon and a siliconoxide of the formula SiOx, wherein 0<x<2 and the silicon oxide isdisposed on the silicon; and heat-treating the reaction gas and thestructure to manufacture the composite.

The carbon source gas may be at least one compound selected from acompound represented by Formula 1, a compound represented by Formula 2,and an oxygen-containing gas represented by Formula 3.C_(n)H_((2n+2−a))[OH]_(a)  Formula 1

In Formula 1, n is an integer of 1 to about 20, for example 1 to about10, and a is an integer of 0 or 1.C_(n)H_((2n))  Formula 2

In Formula 2, n is an integer of 2 to about 6, for example about 3 toabout 5.CxHyOz  Formula 3

In Formula 3, x is an integer of 0 or 1 to about 20, for example about 2to about 15; y is an integer of 0 or 1 to about 20, for example about 2to about 15; and z is an integer of 1 or 2.

The compound represented by Formula 1 and the compound represented byFormula 2 may be least one selected from methane, ethylene, propylene,methanol, ethanol, and propanol.

The oxygen-containing gas represented by Formula 3 may include, forexample, at least one selected from carbon dioxide (CO₂), carbonmonoxide (CO), and water (H₂O).

The method may further include disposing, e.g., supplying, an inert gasthat is at least one selected from nitrogen, helium, and argon inaddition to the carbonaceous source gas.

The oxygen-containing gas may be at least one selected from carbonmonoxide, carbon dioxide, and water vapor.

When the carbon source gas is the oxygen-containing gas, a thickness ofthe silicon oxide may be formed thicker than a thickness of a naturalsilicon oxide. For example, a thickness of the silicon oxide may beselected to be about 10 nm or less, for example, from about 0.1 nm toabout 10 nm, or about 0.5 nm to about 5 nm. When a thickness of thesilicon oxide is within the range above, a shape and a thickness of thegraphene may be suitable. In particular, when a thickness of the siliconoxide layer is formed thicker than a thickness of a natural oxide layer,a graphene layer having a compact structure, as compared to a graphenenanosheet formed on the silicon oxide layer, may be obtained. Here, thegraphene layer has, for example, a 5- or 10-layered structure.

When the gas mixture includes water vapor, the composite obtained as aresult may have a greater conductivity than when water vapor is notincluded. Although not limited to a particular theory, it is understoodthat carbon with a high degree of crystallinity is deposited on thesilicon covered with a silicon oxide by the reaction of the gas mixturein the presence of water vapor, and thus the composite may have a highconductivity even when the silicon is coated with a small amount ofcarbon. A content of water vapor in the gas mixture may be, for example,from about 0.01 volume percent (vol %) to about 10 vol %, for exampleabout 0.05 vol % to about 5 vol %, or about 0.1 vol % to about 1 vol %,based on a total volume of the carbon source gas, but is not limitedthereto.

The carbon source gas may comprise, for example, at least one selectedfrom methane, a gas mixture including methane and an inert gas, anoxygen-containing gas, and a gas mixture including methane and anoxygen-containing gas.

In an embodiment, the carbon source gas may be a gas mixture of CH₄ andCO₂, or a gas mixture of CH₄, CO₂, and H₂O.

The gas mixture of CH₄ and CO₂ may be provided at a molar ratio of about1:0.20 to 0.50, for example, about 1:0.30 to 0.40, for CH₄:CO₂.

The gas mixture of CH₄, CO₂, and H₂O may be provided at a molar ratio ofabout 1:0.20 to 0.50:0.01 to 1.45, for example, about 1:0.25 to0.45:0.10 to 1.35, for example, about 1:0.30 to 0.40:0.50 to 1.0, forCH₄:CO₂:H₂O.

In another embodiment, the carbon source gas may comprise carbonmonoxide and/or carbon dioxide (CO₂).

In another embodiment, the carbon source gas is a gas mixture of CH₄ andN₂.

The gas mixture of CH₄ and N₂ may be provided at a molar ratio of about1:0.20 to 0.50, for example, about 1:0.25 to 0.45, for CH₄:N₂. Forexample, the gas mixture of CH₄ and N₂ may be provided at a molar ratioof about 1:0.30 to 0.40, for CH₄:N₂. In another embodiment, the carbonsource gas may not include an inert gas, such as nitrogen.

The heat-treating of the structure may be performed at a temperature ina range of about 700° C. to about 1100° C., for example, in a range ofabout 700° C. to about 1000° C.

In the heat-treating, a pressure is not limited and may be selected inconsideration of a heat-treating temperature, a composition of a gasmixture, and a desired amount of carbon coating. The pressure for theheat-treating may be selected by changing an amount of supply anddischarge of the gas mixture from the reactor. For example, the pressurefor the heat-treating may be about 1 atmosphere (atm) or higher, forexample, about 2 atm or higher, about 3 atm or higher, about 4 atm orhigher, or about 5 atm or higher, for example about 1 to about 10 atm,but is not limited thereto.

A heat-treating time is not particularly limited but may beappropriately selected depending on a heat-treating temperature, aheat-treating pressure, a composition of a gas mixture, and a desiredamount of carbon coating. For example, the reaction time may be in arange of about 10 minutes to about 100 hours, for example, in a range ofabout 30 minutes to about 90 hours, for example, in a range of about 50minutes to about 40 hours, but is not limited thereto. Although notlimited to a particular theory, since an amount of graphene (carbon)being deposited increases as time passes, electrical properties of thecomposite may be improved accordingly. However, such tendency is notalways in direct proportion to time. For example, no further graphenedeposition may occur or a deposition rate of the graphene may decreaseafter a selected period of time.

The method of manufacturing a composite may provide a uniform coating ofgraphene on the silicon covered with the silicon oxide (SiOx) even at arelatively low temperature though a gas phase reaction of the carbonsource gas. Also, dropout, e.g., delamination, of the graphene formed onthe silicon covered with the silicon oxide (SiOx) layer does notsubstantially occur. When a thickness of the silicon oxide layer issuitable, dropout of the graphene may be even further suppressed. Inthis regard, a thickness of the silicon oxide layer that may efficientlysuppress elimination of the graphene is about 10 nm or less, forexample, from about 0.1 nm to about 10 nm, for example, from about 0.1nm to about 5 nm.

Also, since the graphene is coated on the silicon through the gas phasereaction, a coating layer with a high degree of crystallinity may beformed, and thus when the composite is used as a negative electrodeactive material, a conductivity of the negative electrode activematerial may be increased without changing a structure of the composite.

A process of manufacturing a carbon composite using the compositeaccording to an embodiment may be as follows.

The process includes combining, e.g., mixing, the composite in whichgraphene is formed on silicon covered with a silicon oxide, and acarbon-based material and heat-treating the mixture to manufacture thecarbon composite.

The heat-treating is performed at a temperature in a range of about 700°C. to about 1000° C., for example about 750° C. to about 900° C. When atemperature of the heat-treating is in this range, the carbon compositemay have improved capacity characteristics.

The composite or the carbon composite according to an embodiment may beused in a battery, an illuminant for display, a thermoelectric device,or a biosensor.

According to another aspect, an electrode including the composite or thecarbon composite is provided. The electrode may be an electrode for alithium battery.

The electrode may be a negative electrode.

The composite or the carbon composite may be used as an electrode activematerial, for example, a negative electrode active material. In thisregard, when the composite or the carbon composite is used as a negativeelectrode active material, volume expansion and pulverization of siliconmay be decreased or effectively eliminated. Also, a conductivity of thenegative electrode active material may be improved, and thus a high ratecapability of a lithium battery using the negative electrode activematerial may be improved. Moreover, an amount of graphene coated on thesilicon, which is covered with a silicon oxide, may be minimized, andthus the negative electrode active material having an improved energydensity per volume may be obtained.

A lithium battery containing the composite or a carbon compositeincluding the composite and a carbon-based material is provided.

The negative electrode may be manufactured by using the method describedas follows.

The negative electrode may be formed by molding a negative electrodeactive material composition including, for example, a composite or acarbon composite that is a negative electrode active material, aconducting agent, and a binder in a predetermined shape or coating thenegative electrode active material composition on a current collector,such as a copper foil. The conducting agent may be omitted in thecomposition. Also, the negative electrode active material may be formedas a film on a separator without the current collector.

In particular, the negative electrode active material composition isprepared by mixing the negative electrode active material, a conductingagent, a binder, and a solvent. A negative electrode plate is preparedby directly coating the negative electrode active material compositionon a metal current collector. Alternatively, a negative electrode platemay be prepared by casting the negative electrode active materialcomposition on a separate support and then laminating a film detachedfrom the support on a metal current collector. The negative electrodeactive material may additionally include a second carbon-based negativeelectrode active material which is different from the negative electrodeactive material described above. For example, the second carbon-basednegative electrode active material may be at least one selected fromnatural graphite, artificial graphite, expansion graphite, graphene,carbon black, fullerene soot, carbon nanotubes, and carbon fibers, butis not limited thereto, and any suitable carbon-based negative electrodeactive material available in the art may be used.

Also, the conducting agent may be acetylene black, ketjen black, naturalgraphite, artificial graphite, carbon black, carbon fibers, or a metalpowder of copper, nickel, aluminum, or silver. The conducting agent maybe a conductive material of one type, such as, a polyphenylenederivative, or a mixture of at least two types of conductive materials,but the conducting agent is not limited thereto, and any suitableconducting agent available in the art may be used.

The binder may be a vinylidene fluoride/hexafluoropropylene copolymer,polyvinylidenefluoride (PVDF), polyacrylonitrile,polymethylmethacrylate, polytetrafluoroethylene, a styrene-butadienerubber-based polymer, polyacrylic acid, polyamidimide, polyimide or amixture thereof, but is not limited thereto, and any suitable binderavailable in the art may be used.

The solvent may be at least one selected from N-methylpyrrolidone,acetone, and water, but the solvent is not limited thereto, and anysuitable solvent available in the art may be used.

Contents of the negative electrode active material, the conductingagent, the binder, and the solvent are at levels which can be determinedby one of skill in the art without undue experimentation. At least oneof the binder and the solvent may be omitted depending on use andconfiguration of a lithium battery, if desired.

A lithium battery according to another embodiment includes the negativeelectrode. The lithium battery may be prepared by using the method asfollows.

First, a negative electrode is prepared by using the method ofmanufacturing the negative electrode.

Next, a positive electrode active material, a conducting agent, abinder, and a solvent are combined to prepare a positive electrodeactive material composition. The positive electrode active materialcomposition is coated directly on a metal current collector and dried toprepare a positive electrode plate. Alternatively, a positive electrodeplate may be prepared by casting the positive electrode active materialcomposition on a separate support and then laminating a film detachedfrom the support on a metal current collector.

The positive electrode active material may include at least one selectedfrom the group consisting of a lithium cobalt oxide, a lithium nickelcobalt manganese oxide, a lithium nickel cobalt aluminum oxide, alithium iron phosphate, and a lithium manganese oxide, but the positiveelectrode active material is not limited thereto, and any positiveelectrode active material available in the art may be used.

For example, the positive electrode active material may be a compoundrepresented by any of following formulas.

Li_(a)A_(1−b)R_(b)D₂ (where, 0.90≤a≤1.8, and 0≤b≤0.5);Li_(a)E_(1−b)R_(b)O_(2−c)D_(c) (where, 0.90≤a≤1.8, 0≤b≤0.5, and0≤c≤0.05); LiE_(2−b)R_(b)O_(4−c)D_(c) (where, 0≤b≤0.5 and 0≤c≤0.05);Li_(a)Ni_(1−b−c)Co_(b)R_(c)D_(α) (where, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05,and 0<α≤2); Li_(a)Ni_(1−b−c)Co_(b)R_(c)O_(2−α)X_(α) (where, 0.90≤a≤1.8,0≤b≤0.5, 0≤c≤0.05, and 0<α<2); Li_(a)Ni_(1−b−c)Co_(b)R_(c)O_(2−α)X₂(where, 0.90≤a≤1.8, ≤0≤b 0.5, 0≤c≤0.05, and 0<α<2);Li_(a)Ni_(1−b−c)Mn_(b)R_(c)D_(α) (where, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05,and 0<α≤2); Li_(a)Ni_(1−b−c)Mn_(b)R_(c)O_(2−α)X_(α) (where, 0.90≤a≤1.8,0≤b≤0.5, 0≤c≤0.05, and 0<α<2); Li_(a)Ni_(1−b−c)Mn_(b)R_(c)O_(2−α)X₂(where, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α<2);Li_(a)Ni_(b)E_(c)G_(d)O₂ (where, 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, and0.001≤d≤0.1); Li_(a)Ni_(b)Co_(c)Mn_(d)G_(e)O₂ (where, 0.90≤a≤1.8,0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, and 0.001≤e≤0.1); Li_(a)NiG_(b)O₂ (where,0.90≤a≤1.8 and 0.001≤b≤0.1); Li_(a)CoG_(b)O₂ (where, 0.90≤a≤1.8 and0.001≤b≤0.1); Li_(a)MnG_(b)O₂ (where, 0.90≤a≤1.8 and 0.001≤b≤0.1);Li_(a)Mn₂G_(b)O₄ (where, 0.90≤a≤1.8 and 0.001≤b≤0.1); QO₂; QS₂; LiQS₂;V₂O₅; LiV₂O₅; LiM′O₂; LiNiVO₄; Li_((3−f))J₂(PO₄)₃ (0≤f≤2);Li_((3−f))Fe₂(PO₄)₃ (0≤f≤2); and LiFePO₄

In the formulas, A is Ni, Co, Mn, or a combination thereof; R is Al, Ni,Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combinationthereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or acombination thereof; X is F, S, P, or a combination thereof; G is Al,Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo,Mn, or a combination thereof; M′ is Cr, V, Fe, Sc, Y, or a combinationthereof; and J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

The compound may have a coating layer on a surface thereof or thecompound may be combined with a compound having a coating layer. Thecoating layer may include a coating element compound of an oxide or ahydroxide of a coating element, an oxyhydroxide of a coating element, anoxycarbonate of a coating element, or a hydroxycarbonate of a coatingelement. The compound forming the coating layer may be amorphous orcrystalline. The coating element included in the coating layer may be atleast one selected from Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B,As, and Zr. A process of forming the coating layer may be any suitablecoating method capable of coating the compound by using the elements ina manner that does not negatively affect desirable physical propertiesof the positive electrode active material (e.g., spray coating orimmersion), and since the details of the coating process may bedetermined by those of skill in the art without undue experimentation,additional detailed description of the coating process is omitted.

For example, the compound may be at least one selected from LiNiO₂,LiCoO₂, LiMn_(x)O_(2x) (where, x is 1 or 2), LiNi_(1−x)Mn_(x)O₂ (where,0<x<1), LiNi_(1−x−y)Co_(x)Mn_(y)O₂ (where, 0≤x≤0.5 and 0≤y≤0.5), LiFeO₂,V₂O₅, TiS, and MoS.

In the positive electrode active material composition, the sameconducting agent, binder, and solvent used in the case of the negativeelectrode active material composition may be used. Also, a plasticizermay be further added to the positive electrode active materialcomposition and/or the negative electrode active material composition toform pores in the electrode plate.

Contents of the positive electrode active material, the conductingagent, the binder, and the solvent are at levels which may be determinedby those of skill in the art without undue experimentation. At least oneof the conducting agent, the binder, and the solvent may be omitted ifdesired depending on use and configuration of a lithium battery.

Next, a separator to be inserted between the positive electrode and thenegative electrode is provided. The separator may be any separatorsuitable for a lithium battery. The separator may have a low resistancewith respect to ion movement and an excellent electrolyte containingability. For example, the separator may be at least one selected fromglass fibers, polyester, Teflon, polyethylene, polypropylene, andpolytetrafluoroethylene. The separator may be a non-woven type or awoven type. For example, a rollable separator, such as polyethylene orpolypropylene, is used in a lithium ion battery, and a separator havingan excellent organic electrolyte containing ability may be used in alithium ion polymer battery. For example, the separator may bemanufactured by using the method as follows.

A separator composition is prepared by mixing a polymer resin, a filler,and a solvent. A separator may be formed as the separator composition isdirectly coated and dried on an electrode. Alternatively, the separatorcomposition may be cased and dried on a support, and a film detachedfrom the support may be laminated on an electrode to prepare theseparator.

The polymer resin used in the preparation of the separator is notparticularly limited, and any suitable material used as a binder forelectrode plates may be used. For example, the polymer resin may be atleast one selected from a vinylidenefluoride/hexafluoropropylenecopolymer, polyvinylidenefluoride (PVDF), polyacrylonitrile, andpolymethylmethacrylate.

The separator may include a ceramic composition to improve function ofthe separator as a membrane. For example, the separator may be coated byan oxide or include ceramic particles.

Next, an electrolyte is prepared.

For example, the electrolyte may be an organic electrolyte. Also, theelectrolyte may be solid. For example, the electrolyte may be a boronoxide or lithiumoxynitride, but is not limited thereto, and any suitablesolid electrolyte available in the art may be used. The solidelectrolyte may be formed on the negative electrode by using a method,such as, sputtering.

For example, an organic electrolyte may be prepared. The organicelectrolyte may be prepared by dissolving a lithium salt in an organicsolvent.

The organic solvent may be any suitable organic solvent available in theart. For example, the organic solvent may be at least one selected frompropylenecarbonate, ethylenecarbonate, fluoroethylenecarbonate,butylenecarbonate, dimethylcarbonate, diethylcarbonate,methylethylcarbonate, methylpropylcarbonate, ethylpropylcarbonate,methylisopropylcarbonate, dipropylcarbonate, dibutylcarbonate,benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahyerofuran,γ-butylolactone, dioxolane, 4-methyldioxolane, N,N-dimehtylformamide,N,N-dimethylacetamide, dimethylsulfoxide, dioxane, 1,2-dimethyoxyethane,sulfolane, dichloroethane, chlorobenzene, nitrobenzene,diethyleneglycol, and dimethylether.

The lithium salt may be any lithium salt available in the art. Forexample, the lithium salt may be at least one selected from LiPF₆,LiBF₄, LiSbF₆, LiAsF₆, LiClO₄, LiCF₃SO₃, Li(CF₃SO₂)₂N, LiC₄F₉SO₃,LiAlO₂, LiAlCl₄, LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂) (where, x and yare a natural number), LiCl, and LiI.

As shown in FIG. 2A, a lithium battery 21 includes a positive electrode23, a negative electrode 22, and a separator 24. The positive electrode23, negative electrode 22, and separator 24 are wound or folded andaccommodated in a battery case 25. Then, an organic electrolyte isinjected into the battery case 25, and the battery case 25 is sealedwith a cap assembly 26, thereby completing the lithium battery 21. Thebattery case may have a shape of a cylinder, a box, or a thin film. Forexample, the lithium battery may be a thin film type battery. Thelithium battery may be a lithium ion battery.

The separator 24 may be disposed between the positive electrode 23 andthe negative electrode 22 to form a battery structure. The batterystructures may be stacked in a by-cell structure and immersed in anorganic electrolyte, and the resultant is accommodated in a pouch andsealed therein, thereby completing a lithium ion polymer battery.

Also, a plurality of the battery structures may be stacked and form abattery pack, and the battery pack may be used in any device requiring ahigh capacity and a high output. For example, the battery pack may beused in a laptop, a smartphone, or an electric vehicle.

The lithium battery has an excellent high rate capability and lifecharacteristics and thus may be used in an electric vehicle (EV). Forexample, the lithium battery may be used in a hybrid vehicle, such as, aplug-in hybrid electric vehicle (PHEV).

In another aspect, an electroluminescent device containing the compositeor the carbon composite that includes the composite and a carbon-basedmaterial.

The electroluminescent device is a device using movement of electrons. Aelectroluminescent device includes at least one of a cathode, an emittertip, and an anode distanced apart from the cathode (see, for example,U.S. Pat. No. 7,009,331; U.S. Pat. No. 6,976,897; U.S. Pat. No.6,911,767; and U.S. 2006/0066217, the content of each of which isincorporated herein by reference). Electrons are emitted when a voltageis applied between the cathode and the anode. The electrons move in adirection from the cathode to the anode. The device is not limited tobut may be used for various purposes, such as in an ultrasound vacuumtube device (e.g., an X-ray tube), a power amplifier, an ion gun, ahigh-energy accelerator, a free electron laser, and an electronmicroscope, particularly in a flat panel display. The flat panel displaymay be used as an alternative for a cathode tube. Thus, the flat paneldisplay may be applied to a television and a computer monitor.

The emitter tip may be a composite according to an embodiment of acarbon composite using the composite.

An emitter tip is formed with a semiconductor, which may be a metal suchas molybdenum or a silicon. One of interested areas regarding use of ametal emitter tip is that a control voltage for emission of theelectrons is relatively high as it is about 100 V. Also, since theemitter tip does not have uniformity, a current density between pixelsis not uniform.

When the emitter tip using the composite or the carbon composite isused, electroluminescent emitting characteristics are improved.

In another aspect, a biosensor containing a composite according to anembodiment or a carbon composite including the composite and acarbon-based material is provided.

The composite according to an embodiment or the carbon composite may beused when an electrode for the biosensor is formed.

FIG. 2E is a cross-sectional view illustrating a structure of abiosensor electrode according to an embodiment. Referring to FIG. 2E,the biosensor electrode according to an embodiment includes a substrate310, a first layer 320 including a composite according to an embodimentor a carbon composite according to an embodiment formed on the substrate310, and a second layer 330 formed on the first layer 20. A biomaterial340 is carried or fixed in the second layer 330 in various manners.

The substrate 310 denotes a plate of all types on which graphene may bedeposited or formed, and, in particular, the substrate 310 may be formedof a material selected from the group consisting of glass, plastic,metal, ceramic, and silicon, but a type of the substrate 310 is notlimited as long as graphene may be deposited or formed thereon.

The biomaterial 340 may be at least one selected from an enzyme, anaptamer, a protein, a nucleic acid, a microorganism, a cell, a lipid, ahormone, a DNA, a PNA, and a RNA. Also, the biomaterial 340 may be oneof various biomaterials that are not mentioned in the presentspecification.

Referring to FIG. 2E, the biomaterial 340 may be a specific enzyme, andthe first layer 320 is an electrode for a biosensor that carries thespecific enzyme or uses a fixed layer. Also, in FIG. 2E, the specificenzyme is shown as carried or fixed in the layer, but a location of thespecific enzyme is not limited thereto, and a part of or a entirety ofthe specific enzyme may be protruded on the layer. In this case, sincean enzyme has an excellent substrate specificity and thus hascharacteristics of selectively reacting with a specific molecule in amixture, an analysis material (e.g., blood sugar) reacting with aspecific enzyme may be selectively detected.

In another aspect, a semiconductor device containing the composite orthe carbon composite including the composite and a carbon-based materialis provided.

The composite or the carbon composite may be used as an electrode of thesemiconductor device.

In another aspect, a thermoelectric material containing the composite orthe carbon composite including the composite and a carbon-based materialand a thermoelectric device including the thermoelectric material areprovided.

The thermoelectric material has an improved thermoelectric performancedue to excellent electric characteristics. The thermoelectric materialmay be effectively used in a thermoelectric device, a thermoelectricmodule, or a thermoelectric apparatus.

Performance of a thermoelectric material is defined by a dimensionlessfigure of merit, a ZT value of Equation 1.ZT=(S ² σT)/k  Equation 1

In Equation 1, ZT is a figure of merit, S is a Seebeck coefficient, a isan electrical conductivity, T is an absolute temperature, and k is athermal conductivity.

As shown in Equation 1, in order to increase a ZT value of athermoelectric material, a Seebeck coefficient and an electricalconductivity, or a power factor (S²σ), need to be increased and athermal conductivity needs to be decreased.

The composite or the carbon composite according to an embodimentcontains graphene, and the composite or the carbon composited is usedfor the thermoelectric material. As a result an electric conductivity ofthe thermoelectric material may be high and a thermal conductivity ofthe thermoelectric material may be lowered. Thus, performance of thethermoelectric material may be improved.

In the composite or the carbon composite according to an embodiment,crystallinity and an electron structure at the interface betweengraphene having properties of a metal and a silicon having properties ofa semiconductor change, and thus a Seebeck coefficient increases, andincreases in an electrical conductivity and a charge mobility may beinduced as transfer of charge particles is accelerated. Also, phononscattering at the interface of the graphene and the silicon increases,and thus a thermal conductivity of the thermoelectric material may becontrolled.

As described above, the composite or the carbon composite may beeffectively used as a thermoelectric material. Thus, the thermoelectricmaterial may be molded by using a method, such as a cutting process, tomanufacture a thermoelectric device. The thermoelectric device may be ap-type thermoelectric device. The thermoelectric device denotes thethermoelectric device that is modified in a predetermined shape, forexample, a rectangular shape.

Also, the thermoelectric device may include compositions that bind withan electrode and have a cooling effect due to current supply orcompositions that have power generating effect due to difference in thedevice or temperature.

FIG. 2B illustrates a thermoelectric module including the thermoelectricdevice. As shown in FIG. 2B, an upper electrode 212 (a first electrode)and a lower electrode 222 (a second electrode) are patterned on an upperinsulating substrate 211 and a lower insulating substrate 221. Also, ap-type thermoelectric composition 215 and an n-type thermoelectriccomposition 216 are in contact with the upper electrode 212 and thelower electrode 222. The electrodes 212 and 222 are connected to outsideof the thermoelectric device through lead electrodes 224. The p-typethermoelectric composition 215 may be the thermoelectric device. Then-type thermoelectric composition 216 may be any n-type thermoelectriccomposition known in the art.

The insulating substrates 211 and 221 may be gallium arsenide (GaAs),sapphire, silicon, PYREX, or a quartz substrate. A material of theelectrodes 212 and 222 may be variously selected from copper, aluminum,nickel, gold, and titanium, and a size of the electrodes 212 and 222 maybe variously selected. A method of patterning the electrodes 212 and 222may be any suitable patterning method, for example, a lift offsemiconductor process, a deposition method, or a photolithographymethod.

In an embodiment of the thermoelectric module, as shown in FIGS. 2C and2D, one of the first electrode and the second electrode may be exposedto a heat source. In an embodiment of the thermoelectric module, one ofthe first electrode and the second electrode may be electricallyconnected to a power source or electrically connected to outside of thethermoelectric module, for example, an electric device (e.g., a battery)that consumes or stores electricity.

As an embodiment of the thermoelectric module, one of the firstelectrode and the second electrode may be electrically connected to apower source.

Hereinafter, the present disclosure will be described in further detailwith reference to the following examples. However, these examples arefor illustrative purposes only and are not intended to limit the scope.

EXAMPLES Preparation Example 1 Preparation of Composite

Silicon nanowires (cross-sectional diameter: 50 nm, length: 400 nm)having a silicon oxide (SiOx, wherein 0<x<2) layer formed thereon at athickness of about 0.1 nm was disposed in a reactor. A gas mixture ofCH₄ and N₂ at a flow rate ratio of 30 standard cubic centimeters perminute (sccm):270 sccm (CH₄:N₂) was flowed into the reactor to form anatmosphere of the gas mixture inside the reactor. A pressure formed bythe flow of the gas mixture inside the reactor was 1 atmosphere (atm).Under the gas mixture atmosphere, a temperature in the reactor wasincreased to about 1000° C. (at a rate of rising temperature: about 23°C./min), and the gas mixture was continuously flowed into the reactorwhile the temperature was maintained for 3 hours to performheat-treatment. Subsequently, the product of the heat-treatment wasallowed to cool in the reactor and in the gas mixture for 4 hours, andthus graphene nanosheet was formed on the silicon wires. Then, thesupply of the gas mixture was stopped, and the reactor was cooled toroom temperature (25° C.) to obtain a composite including the siliconnanowires covered with the silicon oxide (SiOx, wherein 0<x<2) layer andhaving the graphene nanosheet formed on the silicon oxide layer.

A content of the graphene nanosheet in the composite was about 8 partsby weight, based on 100 parts by weight of the composite.

Preparation Example 2

A composite including a graphene layer laminated on silicon wirescovered with a silicon oxide (SiOx, wherein 0<x<2) layer was obtained inthe same manner used in Preparation Example 1, except that a gas mixtureof CO₂ and CH₄ at a flow rate ratio of 150 sccm:150 sccm (CO₂:CH₄) wasused instead of the gas mixture of CH₄ and N₂ at a flow rate ratio of 30sccm:270 sccm.

A content of the graphene layer in the composite was about 8 parts byweight, based on 100 parts by weight of the composite.

Preparation Example 3

A composite including a graphene layer laminated on silicon wirescovered with a silicon oxide (SiOx, wherein 0<x<2) layer was obtained inthe same manner used in Preparation Example 1, except that a gas mixtureof H₂O, CO₂, and CH₄ at a flow rate ratio of 0.001 sccm:150 sccm:150sccm (H₂O:CO₂:CH₄) was used instead of the gas mixture of CH₄ and N₂ ata flow rate ratio of 30 sccm:270 sccm.

A content of the graphene layer in the composite was about 8 parts byweight, based on 100 parts by weight of the composite.

Preparation Example 4

A composite including a graphene layer laminated on silicon wirescovered with a silicon oxide (SiOx, wherein 0<x<2) layer was obtained inthe same manner used in Preparation Example 1, except that a gas havingCO at a flow rate 100 sccm was used instead of the gas mixture of CH₄and N₂ at a flow rate ratio of 30 sccm:270 sccm.

A content of the graphene layer in the composite was about 8 parts byweight based on 100 parts by weight of the composite.

Preparation Example 5

A composite including a graphene layer laminated on silicon wirescovered with a silicon oxide (SiOx, wherein 0<x<2) layer was obtained inthe same manner used in Preparation Example 1, except that a gas havingCO₂ at a flow rate of 100 sccm was used instead of the gas mixture ofCH₄ and N₂ at an atomic ratio of 30 sccm:270 sccm.

A content of the graphene layer in the composite was about 8 parts byweight, based on 100 parts by weight of the composite.

Preparation Example 6

A composite including a graphene layer laminated on silicon wirescovered with a silicon oxide (SiOx, where 0<x<2) layer was obtained inthe same manner used in Preparation Example 2, except that a temperatureinside the reactor was changed to 850° C. instead of 1000° C.

A content of the graphene layer in the composite was about 8 parts byweight, based on 100 parts by weight of the composite.

Preparation Example 7

A composite including a graphene layer laminated on silicon wirescovered with a silicon oxide (SiOx, wherein 0<x<2) layer was obtained inthe same manner used in Preparation Example 2, except that a temperatureinside the reactor was changed to 700° C. instead of 1000° C.

A content of the graphene layer in the composite was about 8 parts byweight, based on 100 parts by weight of the composite.

Preparation Example 8

A composite including a graphene nanosheet laminated on siliconnanoparticles covered with a silicon oxide (SiOx, wherein 0<x<2) layerwas obtained in the same manner used in Preparation Example 1, exceptthat silicon nanoparticles (average particle diameter: about 150 nm)having a silicon oxide (SiOx, wherein 0<x<2) layer formed thereon wereused instead of the silicon nanowires. Here, the thickness of thesilicone oxide (SiOx, wherein 0<x<2) nanosheet was about 0.1 mm. Acontent of the graphene nanosheet in the composite was about 8 parts byweight, based on 100 parts by weight of the composite.

Preparation Example 9

A composite including a graphene layer laminated on silicon wirescovered with a silicon oxide (SiOx, wherein 0<x<2) layer was obtained inthe same manner used in Preparation Example 8, except that a gas mixtureof CO₂ and CH₄ at a flow rate ratio of 150 sccm:150 sccm (CO₂:CH₄) wasused instead of the gas mixture of CH₄ and N₂ at a flow rate ratio of 30sccm:270 sccm (CH₄:N₂). A content of the graphene layer in the compositewas about 8 parts by weight, based on 100 parts by weight of thecomposite.

Reference Example 1

A composite including a graphene layer laminated on silicon wirescovered with a silicon oxide (SiOx, wherein 0<x<2) layer was obtained inthe same manner used in Preparation Example 1, except that a gas havingN₂ at a flow rate of 300 sccm was used instead of the gas mixture of CH₄and N₂ at a flow rate ratio of 30 sccm:270 sccm.

Comparative Preparation Example 1

Silicon wires (SiNANOde available from Nanosys, Milpitas, Calif.) onwhich a silicon oxide (SiOx, wherein 0<x<2) natural oxide layer wasformed, was used.

Comparative Preparation Example 2

The silicon nanowires were located in the reactor. Hydrogen was firstflowed into the reactor at a rate of about 300 sccm, a temperatureinside the reactor under the condition was increased to about 1000° C.,and the temperature was maintained for about 2 hours to performheat-treatment.

Subsequently, a gas mixture of CH₄ and H₂ at a flow rate ratio of 100sccm:200 sccm was flowed into the reactor to form an atmosphere of thegas mixture inside the reactor. A pressure formed by the flow of the gasmixture inside the reactor was 1 atm. Under the gas mixture atmosphere,a temperature in the reactor was increased to about 1000° C., and thegas mixture was continuously flowed into the reactor while thetemperature was maintained for 1 hour to perform heat-treatment.

Subsequently, nitrogen was flowed into the reactor at a rate of about300 sccm, and the heat-treatment was performed for about 1 hour whilethe temperature inside the reactor was maintained at about 1000° C., andthen the product of the heat treatment was allowed to cool in thereactor and in the gas mixture for 4 hours without performing theheat-treatment.

Therefore, a silicon carbide coating layer was formed on the siliconwires. Then, the supply of the gas mixture was stopped and the reactorwas cooled to room temperature while nitrogen gas was flowed therein,and thus a structure including the silicon wires and a silicon carbidelayer coating on a surface of the silicon wires was obtained.

Comparative Preparation Example 3

A composite was prepared in the same manner as used in PreparationExample 1, except that a gas having H₂ at a flow rate of 300 sccm wasused instead of the gas mixture of CH₄ and N₂ at a flow rate ratio of 30sccm:270 sccm.

According to Comparative Preparation Example 3, no coating layer wasformed on the silicon wires.

Comparative Preparation Example 4

Silicon nano-sized particles (VD vision, Japan), which are covered witha silicon oxide layer, which is a natural oxide layer, was used.

Comparative Preparation Example 5

Silicon nano-sized particles (VD vision, Japan), which are covered witha silicon oxide layer, which is a natural oxide layer, was located inthe reactor. Hydrogen was first flowed into the reactor at a rate ofabout 300 sccm, a temperature inside the reactor under the condition wasincreased to about 1000° C., and the temperature was maintained forabout 2 hours to perform heat-treatment.

Subsequently, a gas having H₂ at a flow rate of 300 sccm was flowed intothe reactor. A pressure formed by the flow of the gas inside the reactorwas 1 atm. Under the gas atmosphere, a temperature in the reactor wasincreased to about 1000° C., and the gas was continuously flowed intothe reactor while the temperature was maintained for 3 hour to performheat-treatment.

Subsequently, the product of the heat treatment was allowed to cool inthe reactor and in the gas for 4 hours without performing theheat-treatment to prepare silicon nano-sized particles.

According to Comparative Preparation Example 5, no coating layer wasformed on the silicon nano-sized particles.

Example 1: Preparation of Negative Electrode

A slurry was prepared by mixing lithium-substituted polyacrylate(Li-PAA) with the composite prepared in Preparation Example 1. In theslurry, a solid content mixture ratio of the composite prepared inPreparation Example 1 and the Li-PAA was 88:12 weight ratio.

The slurry was coated on a Cu foil, and then a doctor blade was used toform a layer having a thickness of about 40 μm. The layer was vacuumdried at a temperature of 120° C. for 2 hours, and then the driedproduct was pressed to prepare a negative electrode.

Examples 2 to 7: Preparation of Negative Electrodes

Negative electrodes were prepared in the same manner used in Example 1,except that the composites prepared in Preparation Examples 2 to 9 wereused instead of the composite prepared in Preparation Example 1.

Example 8: Preparation of Negative Electrode

A slurry was prepared by mixing the composite prepared in PreparationExample 8, Super P carbon (Timcal), and a lithium-substitutedpolyacrylate (Li-PAA) solution. In the slurry, a weight ratio of thecomposite prepared in Preparation Example 8, Super P carbon, and theLi-PAA was 65:15:20.

The slurry was coated on a Cu foil, and then a doctor blade was used toform a layer having a thickness of about 40 μm. The layer was vacuumdried at a temperature of 120° C. for 2 hours, and then the driedproduct was pressed to prepare a negative electrode.

Example 9: Preparation of Negative Electrode

A negative electrode was prepared in the same manner used in Example 8,except that the composites prepared in Preparation Example 9 was usedinstead of the composite prepared in Preparation Example 8.

Comparative Examples 1-4: Preparation of Negative Electrodes

Negative electrodes were prepared in the same manner used in Example 1,except that the structures prepared in Comparative Preparation Examples1-4 were used instead of the composite prepared in Preparation Example1.

Comparative Example 5 and 6: Preparation of Negative Electrode

A negative electrode was prepared in the same manner used in Example 8,except that the structures prepared in Comparative Preparation Examples1 and 2 was used instead of the composite prepared in PreparationExample 8, respectively.

Comparative Example 7 and 8: Preparation of Negative Electrode

A negative electrodes were prepared in the same manner used in Example8, except that the structures prepared in Comparative PreparationExamples 4 and 5 was used instead of the composite prepared inPreparation Example 8.

Manufacturing Example 1: Manufacture of Coin Cell

A coin cell (CR2032) was manufactured by using the negative electrodeprepared in Example 1 and lithium as a counter electrode.

A separator was a polypropylene layer (Celgard 3510), and an electrolytewas 1.3 molar (M) of LiPH₆ ethylene carbonate:diethylcarbonate:fluoroethylene carbonate (EC:DEC:FEC) at a volume ratio of2:6:2.

Comparative Manufacturing Examples 1-4: Manufacture of Coin Cells

Coin cells were manufactured in the same manner used in ManufactureExample 1, except that the negative electrodes prepared in ComparativeExamples 1-4 were used instead of the negative electrode prepared inExample 1.

Manufacturing Examples 2 to 9: Manufacture of Coin Cells

Coin cells were manufactured in the same manner used in ManufactureExample 1, except that the negative electrodes prepared in Examples 2 to9 were used instead of the negative electrode prepared in Example 1.

Comparative Manufacturing Examples 5 to 8: Manufacture of Coin Cell

A coin cells were manufactured in the same manner used in ManufactureExample 8, except that the negative electrodes prepared in ComparativeExamples 5 to 8 were used instead of the negative electrode prepared inExample 8.

Reference Manufacture Example 1: Manufacture of Coin Cell

A coin cell was manufactured in the same manner used in ManufacturingExample 1, except that the composite negative prepared in ReferenceExample 1 was used instead of the composite prepared in PreparationExample 1.

Evaluation Example 1: Charging and Discharging Characteristics

(1) Measurement of Initial Efficiency, Cycle Property, CoulombicEfficiency, and Discharge Capacity

1) Manufacturing Example 1 and Comparative Manufacture Examples 1 and 2

Charging/discharging characteristics of the coin cells prepared inManufacturing Example 1 and Comparative Manufacturing Examples 1 and 2were evaluated.

The charging/discharging evaluation was performed by charging lithium upto a voltage of 0.001 V, discharging the lithium to a voltage of 1.5 V,and repeatedly measuring up to about 100 cycles to when a specificcapacity of the coin cell decreases to 92% of the performance comparedto specific capacity of the coin cell at the first cycle. The currentwas controlled to be 50 milliamperes (mA) per 1 gram (g) of a weight ofthe electrode.

Also, in order to confirm charging speed characteristics, the coin cellswere charged at a current of 0.5 C and discharged at a current of 0.05C, and the results are shown in Table 1. Moreover, discharge capacitychanges that were measured according to repeated cycles in the coincells prepared in Manufacturing Example 1 and Comparative ManufacturingExamples 1 and 2 each respectively including the negative electrodeprepared in Example 1 and Comparative Examples 1 and 2 are shown in FIG.3.

TABLE 1 1st Cycle Rate Charg- Dis- Initial capability Coulombic ingcharging efficiency 0.5 C/0.05 C efficiency Unit mAh/g mAh/g (%) % %Manufacturing 647.42 552.9 85.4 98.35 99.61 Example 1 Comparative 652.17568.7 87.2 97.19 99.10 Manufacturing Example 1 Comparative 610.73 529.586.7 98.35 99.61 Manufacturing Example 2

Referring to FIG. 3 and Table 1, a capacity and an initial efficiency ofthe coin cell prepared in Manufacturing Example 1 decreased to a degreedue to a graphene characteristic of having a small volume capacitycompared to those of the coin cell prepared in Comparative ManufacturingExample 1. However, because a generation in the SEI layer is lowered, acoulombic efficiency improved, and thus durability of the coin cellprepared in Manufacturing Example 1 was significantly increased. Also, arate capacity due to the increase in graphene conductivity wasincreased. A capacity of the coin cell prepared in ComparativeManufacturing Example 2 was reduced due to SiC formation caused by usinga graphene produced by a chemical vapor deposition (CVD) method, and adurability of the coin cell prepared in Comparative ManufacturingExample 2 significantly decreased.

2) Manufacturing Examples 1 to 5, Comparative Manufacturing Examples 1and 3, and Reference Manufacturing Example 1

Charging/discharging characteristics of the coin cells prepared inManufacturing Examples 1 to 5, Comparative Manufacturing Examples 1 and3, and Reference Manufacture Example 1 were evaluated.

The charging/discharging evaluation was performed by charging the coincell up to a voltage of 0.001 V, discharging the coin cell to a voltageof 1.5 V, and repeatedly measuring up to about 100 cycles to when aspecific capacity of the coin cell decreases to 92% of the performancecompared to specific capacity of the coin cell at the first cycle. Acurrent condition for the evaluation was controlled to be 50 mA per 1 gof a weight of the electrode.

Also, in order to confirm charging speed characteristics, the coin cellswere charged at a current of 0.5 C and discharged at a current of 0.05C, and the results are shown in Table 2. Moreover, discharge capacitychanges that were measured according to repeated cycles in the coincells prepared in Manufacturing Examples 1 to 5, ComparativeManufacturing Examples 1 and 3, and Reference Manufacture Example 1 eachrespectively including the negative electrode prepared in Examples 1 to5, and Comparative Examples 1 and 3, and the composite prepared inReference Example 1 are shown in Table 4. In FIG. 4, “Bare” are resultsfor Comparative Manufacturing Example 1, CH₄ are results forManufacturing Example 1, CO2+CH4 are results for Manufacturing Example2, H2O+CO2+CH4 are results for Manufacturing Example 3, CO are resultsfor Manufacturing Example 4, CO2 are results for Manufacturing Example5, N2 are results for Reference Manufacture Example 1, and H2 areresults for Comparative Manufacturing Example 3.

TABLE 2 1st Cycle Rate Charging Discharging Initial capability Coulombicto 0.05 C to 0.05 C efficiency 0.5 C/0.05 C efficiency Unit mAh/g mAh/g(%) % % Manufacturing 647.42 552.9 85.4 98.35 99.61 Example 1Manufacturing 610.61 517.8 84.8 99.82 99.49 Example 2 Manufacturing593.71 481.5 81.1 98.44 99.57 Example 3 Manufacturing 677.57 573.9 84.798.59 99.61 Example 4 Manufacturing 722.41 606.1 83.9 97.61 99.38Example 5 Comparative 610.73 529.5 86.7 97.19 99.10 ManufacturingExample 1 Comparative 677.14 577.6 85.3 97.91 99.36 ManufacturingExample 3 Reference 735.75 619.5 84.2 98.36 99.47 Manufacture Example 1

Referring to FIG. 4, it may be confirmed that a rate characteristic anda coulombic efficiency of the coin cells prepared in ManufacturingExamples 1 to 5 were improved compared to those of the coin cellsprepared in Comparative Manufacturing Examples 1 and 3.

3) Manufacturing Example 8 and Comparative Manufacturing Examples 7 and8

Charging/discharging characteristics of the coin cells prepared inManufacturing Example 8 and Comparative Manufacturing Examples 7 and 8were evaluated.

The charging/discharging evaluation was performed by charging the coincell up to a voltage of 0.001 V, discharging the coin cell to a voltageof 1.5 V, and repeatedly measuring up to about 30 cycles. A currentcondition for the evaluation was controlled to be 50 mA per 1 g of aweight of the electrode.

Rate capabilities of the coin cells prepared in Manufacturing Example 8and Comparative Manufacturing Examples 7 and 8 were evaluated bycharging/discharging the coin cells at a constant current of 0.1 C, 0.2C, 0.5 C, 1 C, 2 C, 5 C, 10 C, or 20 C, respectively and the results areshown in FIG. 4A.

Referring to FIG. 4A, it may be known that rate performance of the coincell prepared in Manufacturing Example 8 was significantly improvedcompared to those of the coin cells prepared in ComparativeManufacturing Examples 7 and 8.

This remarkable rate performance is attributed to the uniformdistribution of the graphene layers over the entire electrode filmfacilitating efficient electron transport and Li ion diffusion

(2) Battery Lifespan

1) Manufacturing Example 1 and Comparative Manufacturing Example 1 and 2

Capacity change according to increase in the number of cycles withrespect to the coin cells prepared in Manufacturing Example 1 andComparative Manufacturing Example 1 and 2 was observed, and the resultsare shown in FIG. 5.

Referring to FIG. 5, it was confirmed that life characteristics of thecoin cell prepared in Manufacturing Example 1 improved compared to thoseof the coin cells prepared in Comparative Manufacturing Examples 1 and2.

Also, in order to measure cycle lifespans of the coin cells prepared inManufacturing Example 1 and Comparative Manufacturing Example 1 and 2,the coin cells were charged at a current of 0.5 C and discharged at acurrent of 0.05 C, and the results are shown in Table 3. Also, dischargecapacity retention rates according to the cycle repetition in the coincells including the negative electrodes prepared in ManufacturingExample 1 and Comparative Manufacturing Example 1 and 2 were measured.The number of cycles at which capacity for each of the coin cellsreduced to 92% of the initial capacity was measured, and the results areshown in Table 3.

TABLE 3 The number of cycles Manufacturing Example 1 100 ComparativeManufacturing Example 1 34 Comparative Manufacturing Example 2 28

Referring to Table 3, it was confirmed a discharge capacity retentionrate and a lifespan of the coin cell prepared in Manufacturing Example 1improved compared to those of the coin cells prepared in ComparativeManufacturing Examples 1 and 2.

3) Manufacturing Example 1-5, Comparative Manufacturing Example 1 and 3,and Reference Manufacturing Example 1

Change in capacity according to an increase in the number of cycles ofthe coin cells prepared in Manufacturing Example 1-5, ComparativeManufacturing Example 1 and 3, and Reference Manufacturing Example 1 wasobserved, and the results are shown in FIG. 6.

Referring to FIG. 6, lifespan of the coin cells prepared inManufacturing Examples 1 to 5 was improved compared to the coin cellsprepared in Comparative Manufacturing Example 1 and ComparativeManufacturing Example 3.

Also, in order to observe lifespan of the coin cells prepared inManufacturing Example 1 to 5, Comparative Manufacturing Example 1 and 3,and Reference Manufacturing Example 1, the coin cells were charged at acurrent of 0.5 C and discharged at a current of 0.05 C, and the resultsare shown in Table 4. Also, discharge retention rates according to 100cycle repetition of the coin cells including the negative electrodesprepared in Manufacturing Example 1 to 5, Comparative ManufacturingExample 1 and 3, and Reference Manufacturing Example 1 were measured.The number of cycle when the initial lifespan is reduced to 92% wasmeasured and shown in FIG. 6. In FIG. 6, “Bare” are results forComparative Manufacturing Example 1, CH4 are results for ManufacturingExample 1, CO2+CH4 are results for Manufacturing Example 2, H2O+CO2+CH4are results for Manufacturing Example 3, CO are results forManufacturing Example 4, CO2 are results for Manufacturing Example 5, N2are results for Reference Manufacture Example 1, and H2 are results forComparative Manufacturing Example 3.

TABLE 4 Discharge capacity retention rate (%) Manufacturing Example 1 92Manufacturing Example 2 88.1 Manufacturing Example 3 92.8 ManufacturingExample 4 85.6 Manufacturing Example 5 85.4 Comparative ManufacturingExample 1 85 (52 cycles) Comparative Manufacturing Example 3 85.3Reference Manufacture Example 1 86.4

Referring to Table 4, it was confirmed that the discharge capacityretention rates of the coin cells prepared in Manufacturing Examples 1to 5 were improved compared to those of the coin cells prepared inComparative Manufacturing Examples 1 and 3.

4) Manufacturing Examples 8 and 9 and Comparative Manufacturing Example4

Charge/discharge characteristics evaluation was performed on the coincells prepared in Manufacturing Examples 8 and 9 and ComparativeManufacturing Example 4.

Charge/discharge characteristics evaluation was performed on coin cellscharged to 0.001 V and discharged to 1.5 V, and the charge/dischargecycle was repeated 120 times. The charging/discharging conditions wereat the first cycle, the second cycle, the third cycle, and the fourthcycle, to the 120th cycle as follows.

(1) 1^(st) Cycle Discharge: 0.05 C, CC/CV, 0.01 V, 0.02 C/Charge: 0.05C, CC, 1.5 V

(2) 2^(nd) Cycle Discharge: 0.1 C, CC/CV, 0.01 V, 0.05 C/Charge: 0.1 C,CC, 1.0V

(3) 3^(rd) Cycle Discharge: 0.2 C, CC/CV, 0.01 V, 0.05 C/Charge: 0.2,CC, 1.0 V

(4) 4^(th) to 120^(th) Cycle Discharge: 0.5 C, CC/CV, 0.01 V, 0.05C/Charge: 0.5, CC, 1.0 V

TABLE 5 1st Cycle Rate 100^(th) Initial capability Coulombic CycleCharge Discharge efficiency 0.5 C/0.05 C efficiency capacity Unit mAh/gmAh/g (%) % % % Comparative Manufacturing 2341 1883 80.44 77.24 98.1 62Example 4 Manufacturing Example 8 2096 1652 78.82 96.2 99.40 92Manufacturing Example 9 1409 1132 80.31 96.2 99.11 98

Referring to Table 5, capacities and initial efficiencies of the coincells prepared in Manufacturing Examples 8 and 9 were reduced by arelatively small volume capacity of graphene compared to those of thecoin cell prepared of Comparative Manufacturing Example 4, and ageneration in the SEI layer is decreased, and thus durability wassignificantly improved due to an increase in a coulombic efficiency.Also, a rate capability was improved due to an increase in grapheneconductivity. Durability of the coin cell prepared in ComparativeManufacturing Example 4 was significantly decreased.

5) Manufacturing Example 8 and Comparative Manufacturing Examples 7 and8

Charge/discharge characteristics evaluation was performed on the coincells prepared in Manufacturing Example 8 and Comparative ManufacturingExamples 7 and 8.

Charge/discharge characteristics evaluation was performed on coin cellscharged to 0.001 V and discharged to 1.5 V, and the charge/dischargecycle was repeated 200 times. A current condition for the evaluation wascontrolled to be 50 mA per 1 g of a weight of the electrode.

A discharge capacity difference according to the repeated cycles ofcharging/discharging in each of the coin cells prepared in ManufacturingExample 8 and Comparative Manufacturing Examples 7 and 8 was measured,and the results are shown in FIG. 6A.

Referring to FIG. 6A, it may be known that cycle lifespan of the coincell prepared in Manufacturing Example 8 was significantly improvedcompared to those of the coin cells prepared in ComparativeManufacturing Examples 7 and 8.

Evaluation Example 2: Transmission Electron Microscopy (TEM) Analysis 1)Preparation Example 1, and Comparative Preparation Examples 1 and 2

The composites prepared in Preparation Example 1 and the materialsprepared in Comparative Preparation Examples 1 and 2 were analyzed byusing a TEM, and the results are shown in FIGS. 7A, 7B, 8A, 8B, 9A, and9B. FIGS. 7B, 8B, and 9B are images of FIGS. 7A, 8A, and 9A magnified ata higher resolution, respectively.

Titan cubed 60-300 (FEI) was used as an analyzer for the TEM analysis.

Referring to FIGS. 7A and 7B, it was confirmed that the composite ofPreparation Example 1 has a structure of a graphene nanosheet grown on atop of silicon nanowires with a silicon oxide (SiOx) layer is formedthereon. In contrast, the composites prepared in Comparative PreparationExamples 1 and 2 did not have a graphene formed on a top of siliconnanowires shown in FIG. 8A, FIG. 8B and FIG. 9A, and FIG. 9B.

2) Preparation Examples 1 to 5, Comparative Preparation Examples 1 and3, and Reference Example 1

The composites prepared in Preparation Examples 1 to 5, the materialsprepared in Comparative Preparation Examples 1 and 3, and the materialprepared in Reference Example 1 were analyzed by using the TEM, and theresults are shown in FIGS. 7A and 7B. FIG. 10, FIGS. 12A to 17A and 17B.FIG. 11. FIGS. 12B to 17B are images of FIG. 10, FIGS. 12A to 17Amagnified at a higher resolution, respectively.

Referring to FIGS. 7A and 7B, it was confirmed that the compositeprepared in Preparation Example 1 has a structure of a graphenenanosheet grown on a top of silicon nanowires with a silicon oxide(SiOx) layer formed thereon.

Referring to FIGS. 10 and 11, it was confirmed that the compositeprepared in Preparation Example 2 has a structure of a graphene layer ata thickness of about 5 nm grown on a top of silicon nanowires with asilicon oxide (SiOx) layer formed thereon. Referring to FIGS. 12A and12B, it was confirmed that the composite prepared in Preparation Example3 has a structure of a graphene layer at a thickness of about 10 nmgrown on a top of silicon nanowires with a silicon oxide (SiOx) layerformed thereon.

Referring to FIGS. 13A and 13B and FIGS. 17A and 17B, it was confirmedthat the composite prepared in Preparation Example 4 and the materialprepared in Reference Example 1 have a structure of an nonhomogeneousgraphene (3 layers) grown on a top of silicon nanowires with a siliconoxide (SiOx) layer formed thereon.

The composites prepared in Preparation Example 5 was analyzed by using aTEM, and the results are shown in FIGS. 14A and 14B.

On the contrast, referring to FIGS. 15A and 15B, it was confirmed thatthe material prepared in Comparative Preparation Example 1 has astructure of only a silicon oxide (SiOx) present on a top of siliconnanowires. Also, referring to FIGS. 15A and 15B, it was confirmed thatthe material prepared in Comparative Preparation Example 3 only hassilicon nanowires.

1) Thickness of Silicon Oxide Layer

A thickness of a silicon oxide (SiOx) layer, carbon source gasatmosphere, and a type of graphene formed thereon of the compositesprepared in Preparation Examples 1 to 5 and a structure prepared inComparative Preparation Examples 1 and 2 were measured by using a TEM,and the results are shown in Table 6.

TABLE 6 Thickness of a silicon oxide (SiOx) layer (nm) Gas atmosphereType of graphene Preparation 0.1 CH₄ + N₂ Graphene nanosheet Example 1Preparation 2 CO₂ + CH₄ Graphene layer Example 2 (5 nm) Preparation 5H₂O + CO₂ + CH₄ Graphene layer Example 3 (10 nm) Preparation 0.1 COnonhomogenous Example 4 graphene (1 to 2 nm) Preparation 3-5 CO₂ —Example 5 Comparative — — — Preparation Example 1 Comparative — CH₄:H₂—(SiC is present) Preparation Example 2

4) Preparation Example 8

The composite prepared in Preparation Example 8 was analyzed by using aTEM, and the results are shown in FIGS. 8C through 8F.

Titan cubed 60-300 (available from FEI, equipped with double Cscorrectors and Gatan Quantum 965) was used as an analyzer for the TEManalysis.

FIG. 8D is an enlarged view of a region in a white-dotted square in FIG.8C. Referring to FIGS. 8C and 8D, it may be confirmed that graphenenanosheet is formed on a silicon oxide layer.

FIG. 8E shows the result of analysis performed on the composite preparedin Manufacturing Example 8 by using a scanning transmission electronmicroscopy (STEM) analysis in a scanning manner. Also, FIG. 8F is anelectron energy loss spectroscopy (EELS) spectra of the composite ofFIG. 8E. From the EELS spectra, EELS line scans across the particlesconfirmed the presence of an oxide through an intermediate peaksignature in the O1s edge at 108 eV, and intensity of the peak relatedto the oxide diminished toward the center of the particles.

Referring to FIGS. 8D and 8E, it may be confirmed that the compositeprepared in Preparation Example 8 does not include SiC.

Evaluation Example 3: X-Ray Photoelectron Spectroscopy (XPS) Analysis 1)Preparation Example 1 and Comparative Preparation Examples 1 and 2

XPS tests were performed on the composite prepared in PreparationExample 1 and the materials prepared in Comparative Preparation Examples1 and 2 by using a Quantum 2000 instrument (Physical Electronics). TheXPS results of Preparation Example 1 and Comparative PreparationExamples 1 and 2 are shown in FIGS. 18A to 18C. FIG. 18A is a C1sspectrum, FIG. 18B is an O1s spectrum, and FIG. 18C is a Si2p spectrum.

XPS analysis was performed by using a Quantum 2000 (PhysicalElectronics. Inc.) at an acceleration voltage of 0.5 keV to 15 keV, 300W, an energy resolution at about 1.0 eV, a minimum analysis area of 10micrometers, and a sputter rate of 0.1 nm/min.

The results of XPS spectrum compositional analysis of the compositeprepared in Preparation Example 1 and the materials prepared inComparative Preparation Examples 1 and 2 are shown in Table 7.

TABLE 7 Atom % (at %) C1s O1s Si2p C1s/Si2p Preparation Example 1 97.471.27 1.26 77.36 Comparative Preparation 22.21 39.64 38.64 0.58 Example 1Comparative Preparation 21.11 43.79 35.11 0.60 Example 2

From the results of Table 7, the composite of Preparation Example 1showed significant graphene characteristics at the C1s peak, andintegrals of Si2p and O1s peaks informing a Si surface were low sincethe entire Si surface of the composite was coated with graphene.

Also, Si of the material according to the Preparation Example 2 obtainedusing a graphene grown by a CVD method was changed to SiC, and thus theSi surface was not coated with graphene. However, it may be confirmedthat a natural oxide layer and SiO₂ were present on the Si surface ofComparative Preparation Example 1 (Bare sample). A SiOx layer may bemaintained on the Si surface by growing graphene directly on the naturaloxide layer present on the Si surface or by providing both anoxygen-containing gas and CH4 for forming a silicon oxide layer whenforming graphene, and thus formation of SiC may be prevented and thegraphene may be controlled by using a principle of forming graphene.

1) Preparation Examples 1 to 4, Preparation Examples 6 and 7, andComparative Preparation Example 1

XPS tests were performed on the composites prepared in PreparationExamples 1 to 4, the materials prepared in Preparation Examples 7 and 8,and the material prepared in Comparative Preparation Example 1 by usingthe Quantum 2000 (Physical Electronics). The XPS results are shown inFIGS. 19A to 19C. FIG. 19A is a C1s spectrum, FIG. 19B is an O1sspectrum, and FIG. 19C is a Si2p spectrum.

Referring to FIGS. 19A to 19C, it was confirmed that the compositesprepared in Preparation Examples 1 to 4, 6, and 7 had a silicon oxide(SiOx) layer formed on a top of silicon nanowires and a structure havinga silicon oxide (SiOx) layer formed on the silicon nanowires due tosupply of oxide layer reinforcing gas and a SiC layer and grapheneformed thereon.

Evaluation Example 4: Transmission Electron Microscopy-ElectronMicroscopy-Energy Dispersive X-Ray (TEM-EDAX) Analysis 1) PreparationExample 1 and Comparative Preparation Examples 1 and 2

TEM-EDAX analyses were performed on the composite prepared inPreparation Example 1 and the materials prepared in ComparativePreparation Examples 1 and 2. Here, a FEI Titan 80-300 (Philips) wasused to perform the TEM-EDAX analyses.

The analyses results are shown in FIGS. 20A and 20B to 22A and 22B.

FIGS. 20A and 20B showed the TEM-EDAX analysis result of the compositeprepared in Preparation Example 1, FIGS. 21A and 21B showed the TEM-EDAXanalysis result of the material prepared in Comparative PreparationExample 1, and FIGS. 22A and 22B showed the TEM-EDAX analysis result ofthe material prepared in Comparative Preparation Example 2.

Evaluation Example 5: Thermogravimetric Analysis

Thermogravimetric analyses were performed on the composites prepared inPreparation Examples 1 to 3. TA (SDT: TGA+DSC) 2010 TGA/DSC1 (METTLERTOLEDO) was used to perform the thermogravimetric analyses within atemperature range of room temperature to 1600° C.).

The results of the thermogravimetric analyses are as shown in FIG. 23.

Referring to FIG. 23, it was confirmed that an amount of grapheneincluded in the composites prepared in Preparation Examples 1 to 3 wasabout 8 wt %, based on a total weight of the composite.

Evaluation Example 6: X-Ray Diffraction Analysis

X-ray analyses using CuKa were performed on the composites prepared inPreparation Examples 1 to 3 and the material prepared in ComparativePreparation Example 1.

The results of the X-ray analyses are as shown in FIG. 24.

The composites prepared in Preparation Example 1 to 3 had substantiallythe same peaks with the case of Comparative Preparation Example 1. Also,the composites prepared in Preparation Example 1 to 3 had the samesilicon oxide peak as in the case of Comparative Preparation Example 1but did not have a SiC peak.

Evaluation Example 7: Raman Analysis

Raman analyses were performed on the composites prepared in PreparationExamples 1 to 3 and the material prepared in Comparative PreparationExample 1. For comparison with the composites prepared in PreparationExamples 1 to 3, FIG. 25 shows the results of Raman analysis on astructure having graphene formed on a top of a silicon oxide, indicatedas “G@SiO₂” in FIG. 25.

A 2010 Spectra instrument (NT-MDT Development Co.) with a laser systemhaving wavelengths of 473 nm, 633 nm, and 785 nm, a lowest Raman shiftup to about 50 cm⁻¹, and a spatial resolution of about 500 nm was usedto perform the Raman analyses.

The results of the Raman analyses are as shown in FIG. 25. Also, basedon the results of the FIG. 25, an intensity ratio of D peak and G peakwas measured and shown in Table 8.

Graphene had peaks at 1350 cm⁻¹, 1580 cm⁻¹, 2700 cm⁻¹ in a Ramananalytical spectrum, and the peaks provide information about athickness, crystallinity, and a charge doping state. The peak at 1580cm⁻¹ is a peak referred to as “G-mode” which is generated from avibration mode corresponding to stretching of a carbon-carbon bond, andan energy of the G-mode is determined by a density of excess electricalcharge doped by the graphene. Also, the peak at 2700 cm⁻¹ is a peakreferred to as “2D-mode” which is useful in evaluating a thickness ofthe graphene. The peak at 1350 cm⁻¹ is a peak referred to “D-mode” whichis shown when there is a defect in a SP² crystal structure. Also, a D/Gintensity ratio provides information about entropy of crystals of thegraphene.

TABLE 8 D/G intensity ratio Preparation Example 1 1.126053 PreparationExample 2 0.92245 Preparation Example 3 0.798807 G@SiO₂ 1.580708

Referring to FIG. 25 and Table 8, it may be confirmed that crystallinityof the graphene improved as a thickness of the silicon oxide (SiOx)layer increased. Also, the structure having graphene formed on the topof the silicon oxide (SiO2), indicated as “G@SiO₂” had the D/G intensitythat is larger than the case of Preparation Examples 1 to 3, and thus itwas confirmed that crystallinity of the graphene was the lowest and hada great number of defects.

Evaluation Example 8: Scanning Electron Microscope (SEM)

The composites prepared in Preparation Examples 8 and 9 and thestructure prepared in Comparative Preparation Example 4 were analyzed byusing an SEM, and the results are shown in FIGS. 26A to 28B.

FIGS. 26A, 27A, and 28A are each respectively SEM images of thecomposites prepared in Preparation Example 8, Preparation Example 9, andComparative Preparation Example 4, and FIGS. 26B, 26C, 27B, and 28B areeach respectively magnified images of FIGS. 26A, 27A, and 28A.

In reference to FIGS. 26A to 28B, it may be confirmed that thecomposites prepared in Preparation Example 8 and 9 had a silicon oxidelayer and graphene formed on silicon nanoparticles.

Evaluation Example 9: In-Situ TEM Evaluation

The in-situ TEM evaluation was performed by using Titan cubed 60-300(FEI), in which an electrical probing TEM holder is mounted.

The composite prepared in Preparation Example 8 was attached at the endof an Au wire electrode, and a lithium metal was scratched with acleaved Pt/Ir counter electrode. The preparation of the sample wascarried out on the holder in a dry room (−55° C. dew point or less than0.5% RH @ 25° C.) and transported to TEM room. Then, the holder wasquickly inserted to TEM chamber, and the manipulation of the probe tipwas precisely controlled by a piezo-electric motor in order to make aphysical contact between silicon nanoparticles and lithium metal. Then,a constant bias from −0.5 to −5 V and +5 V was applied for lithiationand delithiation, respectively. The microstructure evolution duringlithiation and delithiation was recorded as a movie clip. The overlookof samples were also examined using the field emission scanning electronmicroscopy (Nova NanoSEM 450S, FEI).

The results of the in-situ TEM analysis are shown in FIGS. 29A through29E.

FIG. 29A is a TEM image of the composite particle bound to a surface ofthe Au wire and a Li/LiO₂ electrode, FIG. 29B is a TEM image of thecomposite particle after the first lithiation process, and FIG. 29Cillustrates a schematic view of the lithiated composite particle.

FIG. 29D is a TEM image of a non-defective particle (red-dotted region Ain FIG. 29B), and FIG. 29E is a TEMP image of a defective particle(blue-dotted region B in FIG. 29B). As shown in FIG. 29B, regions A andB are directly in contact with the Li/LiO₂ electrode, and region C isnot directly in contact with the Li/LiO₂ electrode.

In this regard, the volume expansion of particles was in all radialdirections even through the contact point of the composite with thesecond electrode is highly localized. This is because fast lithiumdiffusion through the graphene layers allows lithium ions to diffuse inthe silicon core in a homogenous manner (see FIG. 29A and regions A andB of FIG. 29B).

As shown in FIG. 29C, it may be known that volume expansion of thenon-defective composite particles was in an uniform radial directionafter the lithiation, but structures of the defective compositeparticles were modified after the lithiation, unlike the non-defectiveparticles. In this regard, it may be known that the graphene layer hasexcellent preventing effect on disintegration or pulverization ofsilicon nanoparticles caused by volume expansion of the siliconnanoparticles during lithiation and delithation process, and thatlithium may rapidly diffuse through the graphene layer to behomogenously diffused into the silicon core.

As shown in FIG. 29C, an interlayer spacing between graphene layers inthe sample has increased slightly from about 3.4□ to about 3.9□ which isattributed to lithium intercalation in the graphene layer.

When the graphene layer described above is included in a battery, volumeexpansion of the battery during charging/discharging may reduce, and aclamping layer may be well maintained by using flexibility of thegraphene during the volume expansion, and thus formation of an SEI layermay be effectively suppressed.

As described above, according to the one or more of the aboveembodiments, a composite has a high adherency between silicon andgraphene, and thus a high rate performance may be improved and a volumeexpansion generated when charging and discharging a battery may bereduced by increasing an electric conductivity, a clamping layer may bewell maintained by using flexibility of graphene in a case of volumeexpansion, and thus a charge/discharge durability may be improved byincreasing a charge/discharge efficiency by suppressing formation of anSEI layer.

It should be understood that the exemplary embodiments described hereinshould be considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features, advantages, or aspects within eachembodiment should be considered as available for other similar features,advantages, or aspects in other embodiments.

What is claimed is:
 1. A composite comprising: silicon; silicon oxide ofthe formula SiO_(x) on the silicon, wherein 0<x<2; and graphene directlyon the silicon oxide, wherein the graphene is oriented at an angle ofabout 0° to about 90°, with respect to a surface of the silicon, whereinthe graphene comprises a plurality of graphene nanosheets or a pluralityof graphene layers, and wherein adjacent graphene nanosheets of theplurality of graphene nanosheets or the plurality of graphene layersform an acute angle.
 2. The composite of claim 1, wherein the grapheneis oriented parallel to a surface of the silicon.
 3. The composite ofclaim 1, wherein the graphene is oriented at an angle of about 5° toabout 80°, with respect to the surface of the silicon.
 4. The compositeof claim 3, wherein the graphene is oriented at an angle of about 10° toabout 70°, with respect to the surface of the silicon.
 5. The compositeof claim 1, wherein the silicon oxide has a thickness of about 300 μm orless.
 6. The composite of claim 1, wherein the silicon is in the form ofa nanowire, a nanoparticle, a nanotube, a nanorod, a wafer, ananoribbon, or a combination thereof.
 7. The composite of claim 1,wherein the silicon has a cross-sectional diameter of less than about500 nm.
 8. The composite of claim 7, wherein the silicon has across-sectional diameter of about 10 nm to about 300 nm.
 9. Thecomposite of claim 1, wherein the plurality of graphene nanosheets orthe plurality of graphene layers, which are non-adjacent at a surface ofthe silicon oxide, form an acute angle.
 10. The composite of claim 1,wherein the graphene is present in an amount of about 0.001 part toabout 10 parts by weight, based on 100 parts by weight of the composite.11. The composite of claim 1, wherein a distance between the grapheneand the silicon oxide is about 10 nm or less.
 12. An electrodecomprising the composite of claim
 1. 13. The electrode of claim 12,wherein the composite further comprises a metal oxide or an aluminumfluoride, and the metal oxide is at least one selected from a magnesiumoxide, a manganese oxide, an aluminum oxide, a titanium oxide, azirconium oxide, a tantalum oxide, a tin oxide, and a hafnium oxide. 14.The electrode of claim 12, wherein the electrode further comprises atleast one second carbon-containing negative electrode active material,and the at least one second carbon-containing negative electrode activematerial is at least one of natural graphite, artificial graphite,expansion graphite, graphene, carbon black, fullerene soot, carbonnanotube, or carbon fiber.
 15. The electrode of claim 12, wherein theelectrode further comprises a conducting agent, and wherein theconducting agent is at least one of acetylene black, ketjen black,natural graphite, artificial graphite, carbon black, carbon fiber, or ametal powder of at least one of copper, nickel, aluminum, or silver. 16.A lithium battery comprising the electrode of claim
 12. 17. A devicecomprising the composite of claim
 1. 18. The device of claim 17, whereinthe device is an electroluminescent device, a biosensor, a semiconductordevice, or a thermoelectric device.
 19. A carbon composite comprisingthe composite of claim 1 and a carbonaceous material.
 20. The carboncomposite of claim 19, wherein the carbonaceous material is at least oneof graphene, graphite, or carbon nanotube.
 21. An electrode comprisingthe carbon composite of claim
 19. 22. The electrode of claim 21, whereinthe carbon composite further comprises a metal oxide or an aluminumfluoride , and the metal oxide is at least one selected from a magnesiumoxide, a manganese oxide, an aluminum oxide, a titanium oxide, azirconium oxide, a tantalum oxide, a tin oxide, and a hafnium oxide. 23.A method of manufacturing a composite, the method comprising: contactinga reaction gas to a structure comprising silicon and a silicon oxide ofthe formula SiOx wherein 0<x<2; and heat-treating the reaction gas andthe structure to form graphene on the silicon and manufacture thecomposite, wherein the reaction gas is at least one selected from acompound represented by Formula 1, a compound represented by Formula 2,and an oxygen-containing gas represented by Formula 3:C_(n)H_((2n+2−a))[OH]_(a)  Formula 1 wherein, in Formula 1, n is aninteger of 1 to about 20, and a is an integer of 0 or 1,C_(n)H_((2n))  Formula 2 wherein, in Formula 2, n is an integer of 2 toabout 6, andC_(x)H_(y)O_(z)  Formula 3 wherein, in Formula 3, x is an integer of 0or 1 to about 20, y is 0 or an integer of 1 to about 20, and z is aninteger of 1 or 2, wherein the composite comprises silicon; siliconoxide of the formula SiO_(x) on the silicon, wherein 0<x<2; and graphenedirectly on the silicon oxide, wherein the graphene is oriented at anangle of about 0° to about 90°, with respect to a surface of thesilicon, wherein the graphene comprises a plurality of graphenenanosheets or a plurality of graphene layers, and wherein adjacentgraphene nanosheets of the plurality of graphene nanosheets or theplurality of graphene layers form an acute angle.
 24. The method ofclaim 23, wherein the reaction gas is at least one compound representedby Formula 2 and methane.
 25. The method of claim 24, wherein thereaction gas is methane.
 26. The method of claim 23, wherein theoxygen-containing gas comprises at least one selected from carbondioxide, carbon monoxide, and water.
 27. The method of claim 23, whereinthe heat-treating is performed at a temperature in a range of about 700°C. to about 1100° C.
 28. The method of claim 23, wherein the silicon isin the form of a silicon nanoparticle.
 29. The method of claim 28,wherein the silicon has a cross-sectional diameter of a silicon nanowiremay be less than about 500 nm.
 30. The method of claim 29, wherein thesilicon has a diameter of about 10 nm to about 300 nm.
 31. The method ofclaim 23, wherein the graphene is oriented at an angle of about 10° toabout 70°, with respect to the surface of the silicon nanoparticle. 32.The method of claim 31, wherein the graphene is present in an amount ofabout 0.001 part to about 10 parts by weight, based on 100 parts byweight of the composite.
 33. The method of claim 23, wherein graphenenanosheets, which are non-adjacent at the surface of the siliconnanoparticle, form an acute angle.
 34. A method of manufacturing anegative electrode active material, the method comprising: contacting areaction gas to a structure comprising silicon oxide of the formula SiOxwherein 0<x<2; and heat-treating the reaction gas and the structure toform graphene on the silicon oxide and manufacture the negativeelectrode active material, wherein the reaction gas is at least oneselected from a compound represented by Formula 1, a compoundrepresented by Formula 2, and an oxygen-containing gas represented byFormula 3:C_(n)H_((2n+2−a))[OH]_(a)  Formula 1 wherein, in Formula 1, n is aninteger of 1 to about 20, and a is an integer of 0 or 1,C_(n)H_((2n))  Formula 2 wherein, in Formula 2, n is an integer of 2 toabout 6, andC_(x)H_(y)O_(z)  Formula 3 wherein, in Formula 3, x is an integer of 0or 1 to about 20, y is 0 or an integer of 1 to about 20, and z is aninteger of 1 or 2, wherein the negative active material comprisessilicon; silicon oxide of the formula SiO_(x) on the silicon, wherein0<x<2; and graphene directly on the silicon oxide, wherein the grapheneis oriented at an angle of about 0° to about 90°, with respect to asurface of the silicon, wherein the graphene comprises a plurality ofgraphene nanosheets or a plurality of graphene layers, and whereinadjacent graphene nanosheets or the plurality of graphene layers of theplurality of graphene nanosheets form an acute angle.
 35. The method ofclaim 34, wherein the silicon has a cross-sectional diameter of asilicon nanowire may be less than about 500 nm.